After an unlicensed cell is introduced to Long Term Evolution (LTE), the spectrum does not need to be licensed and can be freely used by any person or any organization because the unlicensed cell uses an unlicensed spectrum. Therefore, before sending data, a network element in an LTE system needs to first perform listen before talk (LBT) to detect whether a channel is occupied. If the channel is occupied, the network element continues to listen on the channel, and does not send the data until detecting that the channel is idle. A base station can start to transmit data provided that the base station detects that a channel is idle. User equipment (UE) can transmit data only when two conditions are met. The first condition is that the UE obtains an uplink resource allocated by the base station and required for data transmission, and the second condition is that the UE performs successful LBT.
The base station may allocate an uplink resource in a licensed-assisted access (LAA) cell to the UE in a subframe m. After obtaining the allocated resource, the UE performs LBT before a subframe m+4 to detect whether a channel is occupied. If the channel is occupied, the LBT fails, and the UE does not send uplink data in the subframe m+4. If the channel is not occupied, the LBT succeeds, and the UE sends uplink data by using the LAA cell in the subframe m+4. The base station receives the uplink data at a preset time-frequency resource location according to a format specified by the base station.
Usually, a base station or UE that uses an LAA cell needs to contend with a Wireless Fidelity (WiFi) device for permission to use a channel, and the WiFi device does not need to know a subframe boundary of an LTE cell. If the UE in the LAA cell starts to perform LBT at a short period before the subframe boundary of the LAA cell, a conflict is likely to occur, and consequently a probability that the UE preempts the channel is relatively low. Therefore, the 3rd Generation Partnership Project (3GPP) determines behavior of the base station/the UE, namely, continuously performing LBT.
However, the base station currently allocates the uplink resource to the UE in a format of an entire subframe. That is, the base station considers, by default, that the UE sends data by using an entire uplink subframe in terms of time, and if the UE preempts only some resources in a subframe, the UE cannot send uplink data.